1. Field of the Invention
This invention relates to a method for the production of maleic anhydride. More particularly, it relates to an improved method for the production of maleic anhydride by the catalytic gas phase oxidation of a raw material gas containing an aliphatic hydrocarbon of not less than 4 carbon atoms and molecular oxygen with a vanadium-phosphorus oxide catalyst. This invention further relates to a method for the activation of the vanadium-phosphorus oxide catalyst. More particularly, it relates to a method for the activation of a vanadium-phosphorus oxide catalyst suitable for the production of maleic anhydride by the catalytic gas phase oxidation of an aliphatic hydrocarbon of not less than 4 carbon atoms with a molecular oxygen-containing gas.
2. Description of the Related Art
It has been well known to produce maleic anhydride by subjecting an aliphatic hydrocarbon of not less than 4 carbon atoms such as, for example, n-butane, to gas phase oxidation in the presence of a vanadium-phosphorus oxide catalyst. Numerous patents have issued to inventions relating to vanadium-phosphorus oxide catalysts and reaction conditions to be used for the production.
As respects the oxidation reaction itself, the practice of selectively oxidizing n-butane, for example, into maleic anhydride by causing a raw material gas containing n-butane and molecular oxygen to contact a vanadium-phosphorus oxide catalyst has been prevailing (as disclosed in U.S. Pat. No. 3,864,280, JP-B-04-4,969, JP-A-05-115,783, U.S. Pat. No. 4,855,459, JP-A-09-3,053, JP-A-07-171,398, U.S. Pat. No. 5,530,144, and U.S. Pat. No. 5,070,060, for example).
This method, however, has been unable to produce the maleic anhydride with satisfactory conversion and selectivity.
Naturally an addition to the yield of the maleic anhydride as a target product brings such a commercial advantage as a reduction in cost. Thus, a further increase in the yield of maleic anhydride has been a constant study theme for researchers in this technical field.
An object of this invention, therefore, is to provide an improved method for the production of maleic anhydride.
Another object of this invention is to provide a method which, in the production of maleic anhydride by the gas phase oxidation of an aliphatic hydrocarbon of not less than 4 carbon atoms in the presence of a vanadium-phosphorus oxide catalyst, allows the maleic anhydride to be produced with a higher yield.
Still another object of this invention is to provide a method which allows effective utilization of an inert gas to be used in the reaction of oxidation.
Yet another object of this invention is to provide a method for the activation of a vanadium-phosphorus oxide catalyst which, in the production of maleic anhydride by the gas phase oxidation of an aliphatic hydrocarbon of not less than 4 carbon atoms in the presence of a vanadium-phosphorus oxide catalyst, allows the maleic anhydride to be produced with a higher yield.